title: Photooxygenation mechanisms in naproxen-amino acid linked systems.
abstract: The photooxygenation of model compounds containing the two enantiomers of naproxen (NPX) covalently linked to histidine (His), tryptophan (Trp) and tyrosine (Tyr) has been investigated by steady state irradiation, fluorescence spectroscopy and laser flash photolysis. The NPX-His systems presented the highest oxygen-mediated photoreactivity. Their fluorescence spectra matched that of isolated NPX and showed a clear quenching by oxygen, leading to a diminished production of the NPX triplet excited state ((3)NPX*-His). Analysis of the NPX-His and NPX-Trp photolysates by UPLC-MS-MS revealed in both cases the formation of two photoproducts, arising from the reaction of singlet oxygen ((1)O2) with the amino acid moiety. The most remarkable feature of NPX-Trp systems was a fast and stereoselective intramolecular fluorescence quenching, which prevented the efficient formation of (3)NPX*-Trp, thus explaining their lower reactivity towards photooxygenation. Finally, the NPX-Tyr systems were nearly unreactive and exhibited photophysical properties essentially coincident with those of the parent NPX. Overall, these results point to a type II photooxygenation mechanism, triggered by generation of (1)O2 from the (3)NPX* chromophore.
authors.affiliation: Departamento de Química/Instituto de Tecnología Química UPV-CSIC, Universitat Politècnica de València, Camino de Vera s/n, E-46022 Valencia, Spain. mcjimene@qim.upv.es mmiranda@qim.upv.es.
authors.forename: Ignacio
authors.initials: I
authors.lastname: Vayá
authors.forename: Inmaculada
authors.initials: I
authors.lastname: Andreu
authors.forename: M Consuelo
authors.initials: MC
authors.lastname: Jiménez
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Miranda
mesh_terms: D000042:Absorption; D000596:Amino Acids / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D009288:Naproxen / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry*; D010782:Photolysis
chemical_list: D000596:Amino Acids; D009288:Naproxen; D010100:Oxygen